User:Roadtechie/Junction Style Guide/Interchanges
Diverging diamond interchange (DDI)
See also: Diverging Diamond Interchange article on Wikipedia.
Diverging diamond interchanges (DDI) are a type of diamond interchange in which the two directions of traffic cross one another on each side of a limited-access roadway. A DDI may pass over or under the limited-access roadway.
This type of interchange is unusual, in that it requires traffic to briefly drive on the opposite side of the road from what is customary for the jurisdiction. However, the design of the Diverging Diamond Interchange controls the driver's line of sight to ensure the cross-over action feels natural and goes unnoticed.
All ramp and surface street segments are set as one-way. If you are creating a DDI along a road which is not divided, divide the road, first.
- For more details on how to properly divide/un-divide a road, see Best map editing practice § Dividing and un-dividing divided highways.
As with all at-grade intersections in Waze, all DDI at-grade intersections are modeled with junction nodes, including the two signaled intersections where opposing directions of traffic "cross over" each other (inner surface road junctions). A DDI may also have two outer surface road junctions, where the one-way segments transition to two-way road segments.
Like with a basic Diamond Interchange, often it will be necessary to represent the ramps making multiple connections to the surface street. Be sure to read the article Simple is better in the Junction Style Guide.
Restrict all non-permitted turns.
There are four junctions in a DDI at which the turn restrictions must be checked - two inner surface road junctions where traffic crosses, and two outer surface road junctions where the road divides/joins on each side of the DDI.
Inner surface road junctions
Disable the two turns from one-way segments to the segments carrying traffic the opposite direction at both inner surface road intersections, for a total of four disabled turns.
Outer surface road junctions
Disable the single turn from the one-way segment carrying traffic exiting the DDI to the one-way segment carrying traffic entering the DDI at both outer surface road intersections, for a total of two disabled turns.
Note on elevations: The surface street segments between the outer most ramps should be either raised or lowered in relation to the freeway segments depending on the actual geography at the interchange.